Pure polyisobutylene (PIB) is a synthetic form of rubber that is a homopolymer of isobutylene and it finds use in many areas of commerce. When the PIB includes groups other than just isobutylene it is still often referred to as PIB when isobutylene is the predominant monomer found in the polymer. Closely related to polyisobutylene is butyl rubber, also a synthetic rubber, which comprises a copolymer of isobutylene and isoprene. In a typical formulation of butyl rubber the composition has 90 to 99.2 mole % isobutylene units and 10 to 0.8 mole % isoprene units. The long segments of polyisobutylene provide excellent flex properties to the butyl rubber. Isobutylene can be polymerized into PIBs having sizes ranging from low molecular weights of 1,000 or less to very high molecular weights of up to 100,000, 400,000 or even higher. Varieties of polyisobutylene are commercially available that are termed highly functionalized PIB, meaning that they include a high percentage of polymer chains that have carbon to carbon double bonds at or very near the terminal ends. One example of such a commercial product is the Glissopal® group of PIBs from BASF which have an alpha-olefin content of greater than 70%. The polyisobutylenes and butyl rubber find use in a wide range of products including in the manufacture of adhesives, fuel cell gaskets, fuel additives, lubricants, agricultural products, paper and pulp, sealing of equipment, caulks, sealants, cling film, and chewing gum. In many of these products and methods of manufacture the polyisobutylene or butyl rubber serves as a starting material that is modified into one or more precursor products that can be further modified to provide useful benefits in the end products. One group of precursor products are polyisobutylenes having one or more primary or secondary hydroxyl functional groups on their terminal ends. These precursors can be further functionalized to include polyurethane segments followed by capping with methacrylate units or they can be directly converted to methacrylate capped polyisobutylenes.
One of the traditional processes for formation of a methacrylate functional PIB is ring opening of PIB succinic anhydride (PIBSA) with hydroxyl functional acrylates or hydroxyl functional methacrylates under base catalysis. The functionality in the methacrylate functionalized product is dependent on the anhydride functionality present in the PIBSA starting material. Commercially available PIBSA is obtained by an ene reaction of a highly functionalized PIB. Many of the highly functionalized PIBs have a mixture of exo double bond and endo double bond content. The endo double bonds are unreactive in the ene reaction, so the PIB acrylate polymer obtained by the typical PIBSA route has a reduced functionality depending on the endo double bond content of the starting material.
One process for formation of terminal alcohol functionalized PIB, especially mono or di alcohol functional PIB, starts with a diallyl functional PIB and subjects it to a hydroboration and oxidation step to produce the alcohol functional PIB. The allyl group comprises a terminal sequence of [—CH2CH═CH2]. Problems with this procedure include considerable processing during the procedure such as multiple filtration steps and solvent exchanges. The resulting alcohol functional PIB often contains undesirable by products of the hydroboration reagents used, for example the reagent 9-borabicyclo[3.3.1.]nonane (9-BBN), which can lead to formation of cyclooctanediol. These by products are difficult to use and must be removed prior to any subsequent reaction steps such as esterification using (meth)acryloyl halide compounds to produce diacrylate PIBs as discussed below. These issues have been handled in the past by incorporating into the procedure multiple washes, solvent exchanges, and multiple filtrations.
Formation of a diacrylate PIB from a diol functional PIB precursor has been accomplished in the past by subjecting the alcohol functional PIB to an esterification reaction using (meth)acryloyl halides to form the di(meth)acrylate PIB. The process esterifies the diol functional PIB using acryloyl chloride and an amine. Problems with this approach include formation of colored products that are difficult to remove, esterification of low molecular weight by products, like cyclooctanediol from the 9-BBN reagent, in the alcohol formation step that may not have been fully removed in the hydroboration step, to cyclooctanediol diacrylate. These cyclooctanediol diacrylates can lead to performance issues in the products that incorporate the diacrylate PIB. So the cleanup procedures in the formation of the diol PIB precursor directly affect the products produced in the esterification step.
It is desirable to provide a simplified method for formation of mono and di alcohol functional PIBs that has fewer by products. It is desirable to create a process that allows for direct use of the alcohol functional PIB in a reaction for formation of polyurethane PIBs capped with acrylate functions or to directly form PIBs capped with acrylate functions.